1. Field of the Invention
The present invention relates to establishment and management of a mobile network by mobile routers, where the mobile network is capable of changing its point of attachment to a wide area network (e.g., the Internet) and thus its reachability in its associated topology.
2. Description of the Related Art
Proposals have been made by Internet Engineering Task Force (IETF) groups for improved mobility support of Internet Protocol (IP) based mobile devices (e.g., laptops, IP phones, personal digital assistants, etc.) in an effort to provide continuous Internet Protocol (IP) based connectivity. For example, the IETF has a Mobile IP Working Group that has developed routing support to permit IP nodes (hosts and routers) using either IPv4 or IPv6 to seamlessly “roam” among IP subnetworks. In addition, the Mobile Networks (MONET) group (renamed as the Network Mobility (NEMO) group) has published different Internet Drafts, available on the World Wide Web at the Network Mobility Home Page at the address http://www.nal.motlabs.com/monet/. One exemplary Internet Draft by Thierry Ernst, entitled “Network Mobility Support Terminology”, February 2002, is available on the World Wide Web at the address: http://www.nal.motlabs.com/monet/drafts/draft-ernst-monet-terminology-01.txt, the disclosure of which is incorporated in its entirety herein by reference.
For example, Ernst describes an exemplary mobile network that can be deployed within an airplane, where passengers establish an IP connection of their respective IP host devices (e.g., laptop, digital telephone, personal digital assistant, etc.) to a mobile router within the airplane for on-board Internet access; during the flight, the mobile router within the aircraft may change its point of attachment to the Internet via distinct Internet Service Providers (ISPs), for example by changing connections via respective radio links or geostationary satellite links for transoceanic flights. Note that a passenger also may have his or her own network (i.e., a personal area network) within the mobile network.
According to the NEMO group, a mobile network may be composed by one or more IP subnets and is connected to the global Internet via one or more Mobile Routers (MR). The mobile router has at least two network interfaces: an egress interface toward the wide area network, and an ingress interface from within the mobile network. Mobile network nodes may include local fixed nodes (LFN) (nodes unable to change their point of attachment while maintaining ongoing sessions), local mobile nodes (LMN) (mobile nodes that belong to the mobile network and able to change their point of attachment within the mobile network or outside the mobile network), and visiting mobile nodes (VMN) (mobile nodes that not belong to the mobile network and that can change their point of attachment from outside the mobile network to inside the mobile network). Each of the nodes may be either a host or a router.
Hence, a mobile router is a router configured for establishing a communication link between the mobile network and an attachment router of a wide area network, such as the Internet, providing connectivity for the mobile network to the wide area network. The mobile router thus serves as a gateway to route packets between the mobile network and the Internet.
The IETF also has a Mobile Ad-hoc Networks (MANET) Working Group that is working to develop standardized MANET routing specification(s) for adoption by the IETF. According to the MANET Working Group, the “mobile ad hoc network” (MANET) is an autonomous system of mobile routers (and associated hosts) connected by wireless links—the union of which form an arbitrary graph. The routers are free to move randomly and organize themselves arbitrarily; thus, the network's wireless topology may change rapidly and unpredictably. Such a network may operate in a standalone fashion, or may be connected to the larger Internet.
The MANET system is particularly suited to low-power radio networks that may exhibit an unstable topology, where wireless propagation characteristics and signal quality between a wireless transmission source and a receiver can be difficult to model and quantify. In a MANET, the device address is tied to the device, not a topological location, as there is no fixed network infrastructure. When the addressed device moves, therefore, the motion changes the routing infrastructure. Hence, as described in an Internet Draft by Baker, entitled “An Outsider's View of MANET”, available from the IETF on the World Wide Web at the address http://www.ietf.org/internet-drafts/draft-baker-manet-review-01.txt (the disclosure of which is incorporated in its entirety herein by reference), the fundamental behavior of a MANET is that a routing node carries with it an address or address prefix, and when it moves, it moves the actual address; when this happens, routing must be recalculated in accordance with the new topology. For example, each mobile router retains its address prefix; hence, neighboring mobile routers in a MANET may have distinct address prefixes.
Although existing MANET protocols focus on the internal connectivity within the unstable topology between mobile devices, the existing MANET protocols suffer from the disadvantage that they provide a poor model for connecting to a wide area network such as the Internet. In particular, MANET proactive protocols allow the mobile nodes to build routing tables for the MANET space, distinct from the routing infrastructure. In addition, existing routing protocols such as Open Shortest Path First (OSPF) Protocol (as specified by the IETF Request for Comments (RFC) 1583), or Intermediate System-to-Intermediate System (IS—IS) protocol (specified by the International Organization for Standardization document ISO 10589) may require up to a minute to converge (i.e., complete protocol communications necessary to establish a connection) and hence not be able to converge quickly enough for a mobile router that is moving from one location to another. For example, in the case of two vehicles passing each other, each having a mobile router, there may exist approximately ten seconds for the mobile routers to establish a connection; hence, routing protocols requiring up to a minute to converge would be unable to establish a connection.
A “Mobile IPv6” protocol is disclosed in an Internet Draft by Johnson et al., entitled “Mobility Support in IPv6”, available on the World Wide Web at the address: http://www.ietf.org/internet-drafts/draft-ietf-mobileip-ipv6-18.txt (the disclosure of which is incorporated in its entirety herein by reference). According to Johnson et al., the Mobile IPv6 protocol enables a mobile node to move from one link to another without changing the mobile node's IP address. Hence, a mobile node is always addressable by its “home address”, an IP address assigned to the mobile node within its home subnet prefix on its home link. Packets may be routed to the mobile node using this address regardless of the mobile node's current point of attachment to the Internet. The mobile node may also continue to communicate with other nodes (stationary or mobile) after moving to a new link. The movement of a mobile node away from its home link is thus transparent to transport and higher-layer protocols and applications.
In addition, Johnson et al. assumes that use of Mobile IPv6 eliminates the need to deploy special routers as “foreign agents” as are used in Mobile IPv4. In Mobile IPv6, mobile nodes make use of IPv6 features, to operate in any location without any special support required from the local router.
Still another protocol is suggested in an Internet Draft by Wakikawa et al., entitled “Global Connectivity for IPv6 Mobile Ad Hoc Networks”, available on the World Wide Web at the address: http://www. ietf.org/internet-drafts/draft-wakikawa-manet-globalv6-01.txt (the disclosure of which is incorporated in its entirety herein by reference). According to Wakikawa et al., a MANET node can obtain a global address from an Internet gateway, and send data to the Internet using a Mobile IPv6 routing header specifying the gateway.
However, requiring all mobile routers to utilize Mobile IPv6 may impose additional processing requirements on the mobile routers, increasing cost and complexity.
Hence, since mobile routers in a MANET may roam rapidly around each other, traditional routing protocols cannot converge rapidly enough to maintain MANET connections for the mobile routers. In addition, since mobile routers in a MANET do not share an address prefix that can be aggregated (i.e., grouped), connectivity to a wide area network such as the Internet becomes problematic. Finally, the boundaries for a given MANET are not precisely defined unless layer 2 access restrictions are imposed, for example using 802.1x authentication.